In recent years, aromatic compounds and heterocyclic compounds having a π-conjugated system have been utilized in various types of electronic devices such as organic electroluminescent devices, cells, semiconductors and the like by use of their emission characteristic and electron or hole transport characteristic.
Organic electroluminescent devices are broadly classified into a polymer device and a low molecular weight device. Especially, with a low molecular weight device, an appropriate degree of carrier mobility and fluorescence emission characteristic are required, which, in turn, requires to freely change a band gap in the development of derivatives of π-conjugated compounds. Moreover, importance is placed on film characteristics of these compounds and, especially, it is required for the compounds to form a stable amorphous film (see Non-patent Document 1, Non-patent Document 2, Non-patent Document 3, and Patent Document 1).
Upon use as a cell, it is required that a compound be controlled in redox potential (see, for example, Non-patent Document 4). Especially, an electrode active substance used in a cell should have a redox potential within a decomposition voltage of a liquid electrolyte, for which it has been accepted as important how to control a redox potential.
With semiconductors, consideration has been generally given to π-conjugated compounds in order to achieve a narrow band gap thereof. However, π-conjugated compounds are ordinarily unlikely to handle because of the low solubility in solvents along with a problem in that structural control is difficult.
Another approach of narrowing a band gap is one wherein π-conjugated systems are two-dimensionally extended (see Non-patent Document 5, Non-patent Document 6). However, these materials are also insoluble in solvents, thus involving inconvenience in handling.
Further, although ordinary π-conjugated polymers behave as an impurity semiconductor by doping, a difficulty is involved in stably preparing semiconductors of both n type and p type from one material.
For a conductive polymer, polymers of aniline and aniline derivatives have been generally in wide use. These polymers are usually synthesized according to an electrolytic polymerization process or chemical polymerization process, and Lewis acid or the like is doped for imparting conductivity thereto. It has been reported (see Patent Document 2) that the aniline polymer obtained in this way is dispersed in water or an organic solvent to provide a varnish, which is coated such as on a substrate by spin coating to provide a thin film, thereby exhibiting very high electric conductivity.
However, aniline polymer is not resistant to oxidation with oxygen in air, with the attendant drawback that the electric conductivity is significantly impaired depending on the degree of oxidation. Additionally, it has been pointed out that upon polymerization, benzidine that is a carcinogenic compound is incorporated as a side product (see Non-patent Document 5, Non-patent Document 7).
Although a polymer of pyrrole is also known as a conductive polymer, this also has a problem in that a difficulty is involved in film formation owing to its insolubility and infusibility, like the aniline polymer.
On the other hand, polythiophene compounds are generally poor in dispersability and solubility in organic or aqueous solvents, with a difficulty in forming a polymer film, dispersion and solution. From a process aspect, these facts present a serious problem in the case of applications as a conductive polymer material.
To cope with this, a hydrocarbon group is introduced into a thiophene monomer at the 3-position thereof, thereby improving solubility in organic solvents of corresponding polythiophene (see Patent Document 3).
According to Bayer, it has been reported that (3,4-ethylenedioxy)thiophene and derivatives thereof are subjected to oxidation polymerization by use of polystyrenesulfonic acid as a dopant to provide a water-solubilized conductive polymer varnish (Patent Document 4).
However, polythiophene-based conductive polymers are very low in solid concentration enabling stable dispersion, with a problem that control in film thickness is difficult.
In this way, hitherto known conductive polymers, respectively, have different problems on the formation of conductive thin films in respect of physical properties. Thus, a novel type of conductive polymer having the possibility of solving these problems has been demanded.
Non-Patent Document 1:                Polymer, Britain, 1983, Vol. 24, p. 748        
Non-Patent Document 2:                Japanese Journal of Applied Physics, 1986, Vol. 25, p. 775        
Non-Patent Document 3:                Applied Physics Letters, United States of America, 1987, Vol. 51, p. 913        
Non-Patent Document 4:                Electrochemistry and Industrial Physicochemistry 1986, Vol. 54, p. 306        
Non-Patent Document 5:                Synthetic Metals, United States of America, 1995, Vol. 69, pp. 599-600        
Non-Patent Document 6:                Journal of the American Chemical Society, United States of America, 1995, Vol. 117, No. 25, pp. 6791-6792        
Non-Patent Document 7:                NEDO Book Archive, Report of the Results of Studies and Developments of Conductive Polymer Materials, March, 1988, pp. 218-251        
Patent Document 1:                U.S. Pat. No. 4,356,429        
Patent Document 2:                U.S. Pat. No. 5,720,903        
Patent Document 3:                JP-A 2003-221434        
Patent Document 4:                JP-A 2002-206022        